Light-emitting element and display device using same

ABSTRACT

A display device includes a plurality of light-emitting elements aligned on a TFT substrate in a formation of a matrix. The plurality of light-emitting elements each have a flat surface portion and including a light-emitting layer, an anode, and a cathode, an insulating layer formed on the TFT substrate and under the light emitting element, and a tilted metal surface provided on a peripheral area surrounding the flat surface portion of the light-emitting element and having a tilt angle with respect to the flat surface portion of the light-emitting element. The tilted metal surface is provided on a surface of a slope of a bank that is provided on the insulation layer, and a width of a cross-section of the bank becomes smaller as the cross section comes farther away from a surface of the TFT substrate. A counter substrate is placed on the TFT substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/589,237, filed on Jan. 5, 2015, which is a continuation of U.S.application Ser. No. 14/327,098, filed on Jul. 9, 2014, now U.S. Pat.No. 8,928,221, which is a continuation of U.S. application Ser. No.14/045,162, filed on Oct. 3, 2013, now U.S. Pat. No. 8,791,632, which isa continuation of U.S. application Ser. No. 13/477,590, filed on May 22,2012, now U.S. Pat. No. 8,558,449, which is a continuation of U.S.application Ser. No. 13/206,915, filed on Aug. 10, 2011, now U.S. Pat.No. 8,193,697, which is a continuation of U.S. application Ser. No.12/631,326, filed on Dec. 4, 2009, now U.S. Pat. No. 8,049,405, which isa continuation of U.S. application Ser. No. 11/852,153, filed on Sep. 7,2007, now U.S. Pat. No. 7,812,515, which is a continuation of U.S.application Ser. No. 11/361,298, filed on Feb. 23, 2006, now U.S. Pat.No. 7,279,833, which is a continuation of U.S. application Ser. No.10/653,623, filed on Sep. 2, 2003, now U.S. Pat. No. 7,030,556, andclaims the benefit of priority under 37 CFR 119 of Japanese applicationno. 2002-360283, filed on Dec. 12, 2002, all of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a light-emitting element and a displaydevice that presents picture images by controlling the light-emissionoperation of the light-emitting element, especially, to a technologythat can be effective to such a light-emitting element as an organiclight-emitting diode and to a display device equipped with the organiclight-emitting diode.

BACKGROUND OF THE INVENTION

An organic light-emitting diode (abbreviated as OLED hereinafter) is adevice that converts electric energy to light energy by injecting holeand electron to a light-emitting layer constructed with an organic thinlayer. A display device constructed with OLED (abbreviated as OLEDdisplay, hereinafter) features the thinness and lightness because noadditional light as backlight is required due to the self light-emittingcapability. Furthermore, OLED display has other features as wide viewingangle and quick time-response in display characteristics.

FIG. 33 shows an example of a conventional OLED construction and asubstantial sectional view of the drawing that explains the displayoperation. This OLED is constructed with transparent electrode 200functioning as an anode, hole transporting layer 103, light-emittinglayer 102, an electron transporting layer 101, a reflective electrode300 made of light-reflective metal that functions as a cathode on atransparent substrate 400, layered in this order. Once a DC voltage isapplied between the transparent electrode 200 and the reflectiveelectrode 300, the holes injected through the transparent electrode 200travels in the hole transporting layer 103, the electrons injectedthrough the reflective electrode 300 travels in the electrontransporting layer 101. Both holes and electrons reach thelight-emitting layer 102 where electron-hole recombination occurs and alight with certain wave length is emitted. A part of the emitted lightfrom the light-emitting layer 102 is observed through the transparentsubstrate 400 by a viewer 1000. The light that emits in roughly parallelto the boundary surface of the layers or the light that has largerincident angle against the boundary surface than the critical anglebetween the two layers thereof is propagated in parallel to the boundarysurfaces and does not travel to the viewer and therefore they are noteffectively used for display lights. The external coupling efficiency(the ratio of amount of the light extracted to the viewer 1000 to theemitted light from the light-emitting layer 102, that, is to say, theratio of external quantum efficiency to internal quantum efficiency) isgenerally estimated to be about 20% on the basis of classical rayoptics. The large amount of the light generated at the light-emittinglayers travels in parallel to the boundary surface of the layers andbecome a loss in the display system. Therefore, in order to realize lowconsumption power and bright OLED, it is quite important to reduce thelight guiding loss and raise the external coupling efficiency.

The references as Patent 1 and Patent 2 shown below describe OLEDs thathave reflection surfaces with the tilted surfaces in order to reduce theguiding loss. For these cases, the description says the light emittedfrom the light-emitting layers travels in parallel or substantiallyparallel to the substrate or the layered film, is reflected at thetilted reflective surface and changes the traveling direction, whichresults into the reduction of light guiding loss and the improvement ofthe external coupling efficiency.

REFERENCES

Patent 1: JP laid-open publication 2001-332388

Patent 2: JP domestic publication 2001-507503

FIG. 34 shows a cross sectional view of an example of conventionalOLEDs. As shown in FIG. 34, a portion of the light which is emitted fromthe organic layer 100 including the light-emitting layer travels inparallel or substantially parallel to the substrate is reflected at thetilted reflective surface (shown as the tilted surface of the electrode300) and then change the propagation direction to the viewer 1000.However the light that is emitted from the light-emitting layer andincidents to the tilted reflective surface is a part of the lightemitted from the light-emitting layer, therefore large part of the lightstill is lost in the traveling and not effectively used. Furthermore, aportion of the light emitted from a pixel of the light-emitting layerdoes not incident to the tilted reflective surface and travels into adifferent pixel, then incident to the tilted reflective surface formedin such a different pixel and change the direction to the viewer. Thismay cause an optical cross-talk and a blur of display. Furthermore, asshown in FIG. 34, when the tilted reflective surface is used as anelectrode for an element of OLED, disconnection failure easily happensat the different step level at the location where the electrode stepsride over the tilted reflective surface.

The objective of this invention is to solve various problems asdescribed above and the light emitted from the light-emitting layercontributes much to the display light and realizes a bright display andthen high quality picture is provided as no blur is generated.Furthermore, other objectives of this invention are to provide faultfree OLED that has no disconnection failure. The other purposes of thisinvention will be clarified in the following descriptions.

SUMMARY OF THE INVENTION

In order to achieve the above purposes, the display device according tothe present invention is a display device having plurality oflight-emitting elements that construct picture elements aligned on asubstrate in a formation of a matrix, wherein the light-emitting elementcomprising a flat surface of a light-emitting layer made at least in aportion therein and a tilted reflective surface at least in a portiontherein, of which the tilted reflective surface is made in theperipheral areas surrounding said surface of a light-emitting layer andhas a tilt angle against the flat surface, wherein an optical waveguidelayer is filled in an area surrounded by said tilted reflective surfaceon said light-emitting layer by which light generated at said lightemitting layer is guided to the peripheral areas and wherein the opticalwaveguide layer is optically isolated from each picture element by thetilted reflective surface. Further more, the tilted reflective surfaceis made on the surface of a slope formed by a bank that is made on saidsubstrate wherein cross sectional width of said bank is narrower againstdistance farther from surface of said substrate, therefore the saidoptical waveguide layer has across sectional formation as a crosssectional width of said optical waveguide layer is wider againstdistance farther from surface of the substrate.

In order to realize an optical waveguide layer that is opticallyisolated from the other picture elements, the height of the tiltedreflective surface from the flat surface of the light-emitting layer islarger than the maximum height of the optical waveguide layer. Or theoptical waveguide layer is formed in a construction as the opticalwaveguide layer is isolated from the other optical waveguide layers foreach picture element.

For this light-emitting element, we can use an organic light-emittingdiode constructed with a reflective electrode that functions as anoptical reflector, a light-emitting layer consisting of an organic layerand a transparent electrode stacked in order from said substrate. Inthis case, it is desirable that the refractive index of the opticalwaveguide layer is larger than that of the air and lower than that ofthe transparent electrode. Furthermore, a sealing material that istransparent against visible light and has gas barrier characteristics isset on a side of the light-emitting layer made on the substrate whereinthe substrate and the sealing material are adhesively bound with a gapthat has substantially same refractive index as the air.

In the display device constructing as described above, the light emittedfrom the light-emitting layer goes into the optical waveguide layer asemitted or passing through the transparent electrode after reflecting onthe reflective electrode. A part of light, among the light incident tothe boundary between the optical waveguide layer and the air gap (wecall the surface of the optical waveguide layer, hereinafter), isreflected with the smaller incident angle than the critical anglehowever the most of the light travels to the viewer with passing throughthe air gap and the sealing material. On the other hand, the part of thelight, among the light incident to the optical waveguide layer, whichhas a larger incident angle to the surface of the optical waveguidelayer is totally reflected at the surface of the optical waveguide layerand travels within the optical waveguide layer in parallel to thesubstrate. The light traveling in the optical waveguide layer comes upto the tilted reflective surface in course of time, the propagationdirection is changed by the reflection thereon and the light that isincident to the surface of the optical waveguide layer with a smallerincident angle than the critical angle partly propagates towards theviewer therefore is effectively used as the display image light.

In short, the light guided in parallel to the substrate thereforeregarded as light loss in the conventional technologies is guided to thetilted reflective surface in a good efficiency and the light extractingratio is improved. In this case, since the optical waveguide layer iscompletely isolated from each other by each picture element, the lightemitted from the light-emitting layer is not guided to the differentpicture elements therefore a display with high picture-quality isrealized without degrading picture-quality seen in optical cross-talk orblur.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross sectional view of a picture element explaining thefirst embodiment of the display device according to the presentinvention.

FIG. 2 is a plan view explaining the first embodiment of the displaydevice according to the present invention.

FIG. 3 is a cross sectional view explaining an example of operation ofthe first embodiment of the display device according to the presentinvention.

FIG. 4 is an explanatory schematic that shows the estimation of theviewing angle characteristics of the light intensity against the slopeangle α.

FIG. 5 is an explanatory schematic of the light traveling in the opticalwaveguide layer in the case that the refractive index of the opticalwaveguide layer is smaller than that of the transparent electrode.

FIG. 6 is an explanatory schematic of the light traveling in the opticalwaveguide layer in the case that the refractive index of the opticalwaveguide layer is larger than that of the transparent electrode.

FIG. 7 is a block diagram showing the whole layout of the embodiment ofthe display device according to the present invention.

FIG. 8 is an equivalent circuit diagram of the active matrix thatcomposes the display device shown in FIG. 7.

FIG. 9 is a layer drawing of the picture element of the embodiment ofthe display device according to the present invention.

FIG. 10 is a cutaway view along B-B line shown in FIG. 9

FIG. 11 is a timing chart of the applied voltage to the gate line.

FIG. 12 is an explanatory schematic of an example of voltage statusamong the gate voltage, the data line voltage and the voltage in thestorage capacitor.

FIGS. 13A-13D schematically show the process to fabricate the bank ofthe display device according to the present invention.

FIG. 14 is a schematic view explaining the bank of the display deviceaccording to the present invention.

FIGS. 15A-15C schematically show the process to fabricate the organiclayer of the device according to the present invention.

FIGS. 16A-16C schematically show the process to fabricate the opticalwaveguide layer of the device according to the present invention.

FIG. 17 is a cross sectional view of a picture element explaining thesecond embodiment of the display device according to the presentinvention.

FIG. 18 is a schematic view explaining the effect of the opticalwaveguide layer in the second embodiment.

FIG. 19 is another schematic view explaining the effect of the opticalwaveguide layer in the second embodiment.

FIG. 20 is a cross sectional view of a picture element explaining thethird embodiment of the display device according to the presentinvention.

FIG. 21 is a cross sectional view of a picture element explaining thefourth embodiment of the display device according to the presentinvention.

FIG. 22 is a cross sectional view of a picture element explaining thefifth embodiment of the display device according to the presentinvention.

FIG. 23 is a cross sectional view of a picture element explaining thesixth embodiment of the display device according to the presentinvention.

FIGS. 24A-24C schematically show the fabrication process of the displaydevice regarding the sixth embodiment shown in FIG. 23.

FIGS. 25A-25C schematically show the fabrication process of the displaydevice regarding the sixth embodiment shown in FIG. 23.

FIG. 26 is a cross sectional view of the picture element explaining thesix embodiment of the display device according to the present invention.

FIG. 27 is a plan view of a picture element explaining the seventhembodiment of the display device according to the present invention.

FIG. 28 is a cutaway view along C-C line shown in FIG. 27.

FIG. 29 is a cutaway view along C-C line shown in FIG. 27 wherein thesixth invention shown in FIG. 23 is applied to the invention embodied asshown in the FIG. 27.

FIG. 30 is a cross sectional view of a picture element explaining theeighth embodiment of the display device according to the presentinvention.

FIG. 31 is a plan view of a picture element explaining the eighthembodiment of the display device according to the present invention.

FIG. 32 is across sectional view of a picture element explaining theninth embodiment of the display device according to the presentinvention.

FIG. 33 is a schematic to shown an example of the construction and thedisplay operation regarding the conventional OLED.

FIG. 34 schematically shows an example of a cross sectional view of theconventional OLED.

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter, exemplary embodiments of this invention will be discussedin conjunction with the drawings as needed.

The First Embodiment

FIG. 1 shows the cross sectional view of one picture element explainingthe first embodiment of this invention. FIG. 2 shows another drawingexplaining the first embodiment. FIG. 1 corresponds to the cutaway viewalong the line of A-A in FIG. 2. One color picture element consists ofthree picture elements of red-light-emitting picture element 20R,green-light-emitting picture element 20G and blue-light-emitting pictureelement 20B which are arranged in side-by-side as shown in FIG. 2 andthe predetermined color is presented by additive color mixing of thelights emitted from these three picture elements. In addition, thesepicture elements 20R, 20G and 20B are called as unit picture elements orsub-pixels and a unit picture element corresponds to a mono-chromaticpicture element for the case of mono-chromatic display device.

For the display device according to the present invention, wires,switching elements, storage capacitors and insulating layers formed onthe substrate as appropriate, however they are not shown in thedrawings. Reflective electrodes 300 consisting of conduction materialwith optical reflecting characteristics that are formed on the substratein a form of an island as corresponding to the picture element and banks500 made of insulator material are formed as covering edges ofreflective electrodes 300 at the peripheral areas thereof. The bank 500has a cross sectional formation in a shape as the width is gettingnarrow as getting farther from the substrate 800 and has tilted surfacesat its side areas. On the part of the tilted surface and the reflectiveelectrode, an organic layer 100 that includes the light-emitting layerformed in each picture element in a form of an island and furthermore atransparent electrode 200 is formed thereon.

The transparent electrode 200 and the reflective electrode 300 functionas an anode (or cathode) and a cathode (or anode), respectively andcomposes an organic light emitting diode with an organic layer 100formed on these electrodes. The organic layer 100 is constructed inthree layered forms as an electron transporting layer, a light-emittinglayer and a hole transporting layer in order from the cathode side or intwo layered form as a single layer functioning as light-emitting andelectron transporting by using a material of dual use. Furthermore, theconstruction of the organic light emitting diode, that has an additionalanodic buffer layer between the anode and the hole transporting layer,can be used.

A tilted reflective surface 700 consisting of optical reflective metalis formed on the transparent electrode 200 and on the locationcorresponding to the surface of a slope formed by a bank 500.Furthermore, an optical waveguide layer 600 that is transparent to thevisible lights and that is composed by a material that has a largerrefractive index than that of the air is filled in the basin-like areasurrounded by the tilted reflective surface 700. Moreover, since theorganic layer 100 is usually degraded by the moisture included in theair, it is desirable that it should be sealed by a seal-off means fromthe open air so that it is not exposed to the open air. In this case, aconstruction such that the bank 500 works as spacer and a seal-offmaterial 900 and the substrate 800 are fixed by an adhesive sealmaterial cemented in a frame-like form around the display portion of thedisplay device is shown.

A glass plate, a plastic film post-processed for gas barrier or alayered plate with thin glass and plastic film can be used for theseal-off material 900. For this construction, it is important to set agap 950 which has the similar refractive index to the air between theseal-off material 900 and the optical waveguide layer 600. Because ifthe seal-off material 900 and the optical waveguide layer 600 contacteach other then the light emitted from the organic layer 100 andpropagating in the optical waveguide layer 600 comes into the seal-offis material 900 and does not come up to the viewer 1000 as resulting ina loss or travels into other picture element and comes up to the viewer1000 thereafter as resulting into, problems of cross-talk and blur.

Inert gas as nitrogen gas may be enclosed in the gap 950, and theassembly is done as nitrogen gas is enclosed and the seal-off materialand the substrate 800 are bound in air-tight. Furthermore, setting gap950 implies that the optical waveguide layer 600 does not contact to theseal-off material 900 and preferably the gap 950 should be set largerthan the distance over which the light cannot travels from the opticalwaveguide layer 600 to the seal-off material 900 due to the tunnelingphenomenon of photons. Since the tunneling phenomenon occurs for a gapshorter than the wavelength of visible light and the gap 950 more than 1μm is sufficient.

Moreover, it is important to keep the height H2 from a flat surface 25of the organic light emitting diode which is from the reflectiveelectrode 300 to the optical waveguide layer 600 smaller than the heightH1 at the upper end of the tilted reflective surface 700. The reason isfrom the optical cross-talk and blur that are caused by the phenomenathat the light emitted from the organic layer 100 traveling in theoptical waveguide layer 600 may propagate over the tilted reflectivesurface 700 for the case when the height H2 of the optical waveguidelayer 600 is larger than the height H1 of the tiled reflective surface700, invade into different picture elements and then externally traveltherefrom. Furthermore, for the case when the flat seal-off material 900is set as the bank 500 used as a spacer, the optical waveguide layer 600contacts the seal-off material 900 unless H1>H2 is kept then the lightinvading from the optical waveguide layer 600 to the seal-off material900 causes problems as reduction of the external coupling efficiency,optical cross-talk and blur.

FIG. 3 is a cross sectional drawing to explain an example of operationfor the first embodiment of the display device according to the presentinvention. Once DC voltage is applied to the transparent electrode 200and the reflective electrode 300 in response to the picture signal, theholes injected through the anode travel in the hole transporting layerand electrons injected trough the cathode travel in the electrontransporting layer, respectively, and both holes and electrons reach tothe emitting layer. The recombination of an electron and a hole occursin the emitting layer and light emission is taken place. The lightemitted from the light emitting layer that constructs the organic layer100 comes into the optical waveguide layer 600 through the transparentelectrode 200 as is emitted or after reflected at the reflectiveelectrode 300. The lights, among the lights coming into the opticalwaveguide layer 600, that come to the boundary between the opticalwaveguide layer 600 and the gap 950 with a smaller incident angle thanthe critical angle partly reflects but mostly come up to the viewerafter passing through the gap 950 and the seal-off material 900 which isnot shown, and are used as display image lights 2000.

On the other hand, the lights coming onto the surface of the opticalwaveguide layer 600 with a larger angle than the critical angle istotally reflected at the surface of the optical waveguide layer 600 andpropagates in the optical waveguide layer 600 in parallel to the surfaceof the substrate 800. The light traveling in the optical waveguide layer600 finally comes to the tilted reflective surface 700, the direction ofthe propagation changes by the reflection, a part of lights that comeinto the surface of the optical waveguide layer 600 with smallerincident angle than the critical angle comes to the viewer and areeffectively used as display image light 2001. In other wards, the lighttraveling in parallel to the substrate 800 resulting in a loss in theconventional technology is led to the tilted reflective surface 700 bythe optical waveguide layer 600 and changes the propagation direction bythe reflection at the tilted reflective surface 700. Then, since thelight is effectively used as the display image light, the externalcoupling efficiency has been improved. For this case, since the opticalwaveguide layer 600 is completely isolated, the light emitted from anorganic layer of a certain picture element does not propagate in otherdifferent picture elements and no problem as optical cross-talk or blurof presentation occurs.

The improvement of the external coupling efficiency by suppression oflight loss due to above propagation becomes more as the ticker opticalwaveguide layer in comparison to the area of the light-emitting portionis made. In other words, though the portion of the flat surface 25 isthe light-emitting area, the thicker the optical waveguide layer 600 is,the higher the external coupling efficiency can be. The reason is asfollows.

The light guided in the optical waveguide layer 600 mainly travels tothe tilted reflective surface 700 with repeating the reflection at thesurface of the optical waveguide layer 600 and that at the reflectiveelectrode 300. For this case, since the reflectance of the reflectiveelectrode 300 is not 100%, usually, the light is partly absorbed andlost by reflective electrode. Therefore, if the number of times for thereflection at the reflective electrode 300 until the light guided in theoptical waveguide layer 600 comes to the tilted reflective surface 700can be reduced, the optical loss by the reflective electrode 300 becomesless and high efficiency of the light extraction from the display can beobtained. Moreover, since no guiding of the light in the opticalwaveguide layer can provide no improvement of external couplingefficiency, the thickness of the optical waveguide layer should belarger than the wavelength of the light so that the good propagation ofthe light is obtained. For this purpose, the thickness of the opticalwaveguide layer should be larger than 1 μm.

As shown in FIG. 2, if the length H in the up-down orientation is longerthan the length W in the left-right orientation in the plane of theemitting area, then the relation as (H2/W)>(H2/H) is obtained. In thiscase the external coupling efficiency for the left-right orientation ishigher than that for the up-down orientation and the viewing angle iswider in right-left orientation than in up-down orientation. This factis useful because the wider viewing angle in the right-left orientationis preferred than that of the up-down orientation and the limited lighthas to be served to the viewers. In other words, the conventional OLEDdisplay has an isotropic viewing angle for the light intensity which isuniform for every direction, however this invention can control theviewing angle characteristics of the light intensity by controlling theratio of the thickness of the optical waveguide layer to the length ofthe light emitting area for the specific orientation. Therefore we canrealize the optimum light intensity characteristic for each particularapplication of the display devices.

In stead of this case, the viewing angle characteristics against thelight intensity can be controlled by the tilt angle .alpha. of thetilted reflective surface 700 against the surface (substrate surface)that is a flat surface 25 in this invention. FIG. 4 shows the schematicsdiagram of the viewing angle characteristics against the light intensityas a function of the tilt angle α of the tilted reflective surface 700.FIG. 4 is provided for the case of the ratio H2/W=0.1 for the length W(see FIG. 2) of the light emitting area and the thickness H2 of theoptical waveguide layer 600 (see FIG. 1) and the refractive index 1.5for the optical waveguide layer and shows the estimation results fortwo-dimensional model. The horizontal axis shows the viewing angle andthe vertical axis shows the relative light intensity normalized to thelight intensity obtained at the front position (intensity at 0° viewingangle) by the conventional OLED that has flat and plane layeredconstruction. As shown in this diagram, the viewing anglecharacteristics of the light intensity can be changed by changing thetilt angle α. For example, we can see the high light intensity at thefront direction and the adjacent direction is obtained for α=23°˜30°,almost constant light intensity characteristics for wide range ofviewing angle for α=45° and the viewing angle characteristics asremarkably decreasing over 50° viewing angle for α=60°.

The tilted reflective surface is not the slope surface constructed in acomplete flat surface for actual cases, the tilt angle α tends not to beconstant over the tilted reflective surface and to constantly vary inaccordance with the location of the tilted reflective surface.Therefore, for the application as the display device for portable phoneswhich a single person mostly uses at a time, wide viewing angle is notrequested but high intensity at the front direction is preferred.Therefore the average angle values for the tilt angle α should beset as20°˜30° and the higher intensity at the front orientation in comparisonto the inclined orientation against the front orientation is preferred,reversely, the wider viewing angle and the brighter picture image arepreferred with the average value of a to approximately be 45° for the TVset applications wherein the display watched by many people. Inaddition, since the present estimation is the calculated result providedin a limited condition under a simple two-dimensional model, the resultcannot be used for the exact quantitative evaluation but be effectivefor the relative evaluation in a qualitative study.

Next, we explain the relation between the refractive indices of opticalwaveguide layer 600 and transparent electrode 200. FIG. 5 and FIG. 6 arethe schematics to explain the effect against the external couplingefficiency. FIG. 5 is for the case that the refractive index of theoptical waveguide layer is smaller than that of the transparentelectrode and FIG. 6 is for the case that the refractive index of theoptical waveguide layer is larger than that of the transparentelectrode. Once we define the refractive index of the transparentelectrode n1, that of the optical waveguide layer n2, incidental angleθ1 of the light from the transparent electrode to the optical waveguidelayer and refraction angle θ2, we obtain sin θ1/sin θ2=n2/n1 fromSnell's law. Therefore, for the case when the refractive index n1 of theoptical waveguide layer 600 is smaller than the refractive index n2 ofthe transparent electrode, the refraction angle θ2 is larger than theincident angle θ1.

On the other hand, when the refractive index n1 of the optical waveguidelayer 600 is larger than the refractive index n2 of the transparentelectrode, the refraction angle θ2 is smaller than the incident angleθ1. Therefore, if we define the propagation distance without reflectionin the optical waveguide layer 600 as L1 for the case of n1>n2 and L2for n1<n2, L1 is larger than L2. The fact that the propagation lengthwithout reflection of the light traveling in the optical waveguide layer600 is long implies that the times of reflection at the reflectiveelectrode 300 until the light traveling up to the tilted reflectivesurface 700, therefore it means the light loss by the absorption by thereflective electrode becomes less. For this reason, it is desirable tokeep the refractive index of the optical waveguide layer less than thatof the transparent electrode for the purpose of improving the externalcoupling efficiency. It should be noted that a critical angle existsbetween the transparent electrode 200 and the optical waveguide layer600 and the light with larger incident angle from the transparentelectrode to the optical waveguide layer is totally reflected and cannotbe led to the optical waveguide layer 600.

Reversely, the critical angle does not exist for the case of n1<n2,therefore the incident angle which even becomes to be the critical anglefor the case of n1>n2, the light can be led from the transparentelectrode to the optical waveguide layer. However, since such a light istotally reflected at the surface of the optical waveguide layer 600 andreturns back to the reflective electrode 300, the light is repeatedlyreflected by the surface of the optical waveguide layer 600 and thereflective electrode 300 and is lost by the decay. To prevent thisphenomenon, it is necessary to increase the thickness of the opticalwaveguide layer by which the times of reflection of the light at thereflective surface 300 can be reduced until the light reaches to thetilted reflective surface 700 while traveling in the optical waveguidelayer. However, in general, the refractive index of the transparentelectrode 200 is rather high as 1.8 to 2.2 and it takes long time toform a transparent material (titanium oxide, for instance) that haslarger refractive index than this in a thickness of an order of micronmeters without damage onto the organic layer therefore such formation isnot industrially desirable. Therefore, it is desirable that therefractive index of the optical waveguide layer should be larger thanthat of the air and less than that of the transparent electrode and theoptical waveguide layer be made of a transparent plastic material thatis relatively formed in ease. For this purpose, it is practical andrealistic to select the refractive index of the optical waveguide layerbe 1.3 to 1.7.

Next, we explain an embodiment of the display device with reference tothe schematics. FIG. 7 shows a schematic of the whole layout of theembodiment. FIG. 8 is an equivalent circuit of the active matrixconstructed on the display portion 2. As shown in FIG. 7, the displaydevice 1 has a display portion 2 at the substantially center of thesubstrate 800. In this display portion 2, a data driver circuit tooutput the picture signals to a plurality of data lines 7 is constructedin the upper part of the display portion and a scan driver circuit tooutput the scan signals to a plurality of gate lines 8. The drivercircuits 3 and 4 comprise shift register circuits, level shiftercircuits and analogue circuits which are composed of P channel and Nchannel TFTs (Thin Film Transistors) in a complementary configuration.The line 9 is a common voltage line.

In this display device 1, being same as active matrix liquid crystaldisplay devices, a plurality of gate lines and that of data lines areset in crossing over in the direction of the expansion and the pictureelement 20 is set at each cross point of gate lines G1, G2, . . . , Gmand data lines D1, D2, . . . , Dn. Each picture element is composed of alight-emitting element 24 consisting of an OLED, storage capacitor 23, aswitching transistor 21 of an N channel TFT of which gate electrode isconnected to the gate line, either a source or a drain electrode to thedata line and the other to the storage capacitor 23 and a drivertransistor 22 of an N channel TFT of which the gate electrode isconnected to the storage capacitor 23, the source electrode is connectedto the common voltage line 9 extending in the same direction as the datalines and the drain electrode is connected to the cathode of an OLEDthat composes the light-emitting element 24. Moreover, the anode of anOLED that constructs a light-emitting element 24 is connected to acurrent supply line commonly used for all picture elements and kept inthe same voltage Va. The light-emitting element 24 emits any of red-,green- or blue-lights and is aligned in a predetermined order in amatrix formation.

In the above construction, once the switching transistor 21 is “ON”state, then the picture signal is written in the storage capacitor 23through the switching transistor 21. Therefore the gate electrode of thedriver transistor 22 is kept in a voltage corresponding to the picturesignal by the storage capacitor 23 even the switching transistor 21 isset to be “OFF” state. The driver transistor 22 is kept in a sourcefollower mode which features constant current characteristics and thelight-emitting operation is maintained since the current from thecurrent supply line flows to the organic light-emitting diode thatconstructs the light-emitting element 24. For this case, the intensityof the emitted light depends on the data written in the storagecapacitor 23. The cease of the emission is realized by setting thedriver transistor 22 “OFF” state.

We explain the construction of the display device regarding the firstembodiment of this invention with referring to a combination of FIG. 9and FIG. 10 and that of FIG. 1 and FIG. 2. FIG. 9 is a layer drawing ofthe picture element showing the constructing layers. FIG. 10 shows acutaway view along the line B-B in FIG. 9. The display device in thisembodiment is constructed as that driver elements (thin film transistorsin this embodiment) as switching transistors and driver transistors andelements connected to those driver elements as gate lines, data lines, acommon voltage line and storage capacitor are formed on a flat substrate800 as glass and insulation layer 30 is formed thereover. On theinsulation layer 30, a reflective electrode 300 that works as a cathodeof the light-emitting element 24 is formed in a shape of an island andthe reflective electrode 300 is connected to the drain electrode 26 ofthe driver transistor via a contact hole 31 opened in the insulationlayer 30.

In this embodiment, the reflective electrode 300 functions as a cathode.For the cathode, the metals of low work function as aluminum, magnesium,magnesium-silver alloy; aluminum-lithium alloy, etc. can be used. Sincethe configuration of a single metal layer using as aluminum needs highdriving voltage and the life-time of the display device is short, aultra-thin film of Li compound (as lithium oxide Li2O, lithium fluorideLiF) formed between the reflective electrode and the organic layer maybe used which equivalently works as aluminum-lithium alloy.Alternatively, the cathode surface contacting with the organic layer isdoped with high reactive metal as lithium or strontium and then lowdrive voltage may be obtained. In addition, the reflective electrode isdesired to be made of highly optical reflective material in order toobtain the high usage efficiency of the light for viewing image.

In the area on which the driver elements and signal lines are formed, abank 500 which overlays these elements and lines and surrounds the flatarea of the reflective electrode 300 is formed thereon. In this case,the bank 500 is formed to cover the contact hole 31. In other words, thecontact hole is desired to be aligned and formed underneath the bank.This helps to be effective to realize higher intensity of light emissionbecause the step difference exists on the contact hole 31 resulting inno use area against light emitting area and we can obtain the widerlight-emitting area by arranging the no light emitting area under thebank area. Moreover, it is desirable that the bank is formed to overlaythe peripheral part of the reflective electrode 300. Because the organiclayer 100 and the transparent electrode 200 are cracked by the stepdifference of the reflective electrode 300 at the peripheral part sothat the transparent electrode 200 is electrically broken and/or thereflective electrode 300 and the transparent electrode 200 areelectrically shorted. Instead of these problems, the overlay forming ofthe bank, therefore, prevents such incidental troubles.

The bank 500 can be formed by patterning an insulator material withphotolithography technology. Inorganic material as silicon oxide,silicon nitride or dielectric material such as acrylic resin andpolyimide resin may be used. In addition, it is preferred that theheight of the bank is more than a few micron meters in order to realizehigh external coupling efficiency since the dimension of the bank 500determines the height of the tilted reflective surface 700 and thethickness of the optical waveguide layer 600. The organic material isrealistic and preferred for such dimensional height of the bank formedin short time processing. The cross sectional view of the bank 500 has atrapezoidal shape so that the horizontal width is less while the heightis farther from the substrate and the side surfaces of the bank has anarrangement into a tilted surface against the substrate surface.Moreover, the bank 500 may be made by other processes provided we canobtain the designed tilted surface as screen printing method and directprinting such as the ink-jet printing.

The organic layer 100 that has light-emitting layer emitting each ofred, green and blue lights is patterned in each predetermined positionfor each picture element in a shape of an island. A transparentelectrode 200 functioning as an anode is formed over the display portion2. The transparent electrode material that has high work function, forexample, ITO (Indium Tin Oxide) is preferable and IZO (Indium ZincOxide) is usable.

The transparent electrode 200 is connected with the current supply line.For the organic layer 100, a material that emits the light in a designedcolor is used and the construction of three layers as an electrontransporting layer, a light-emitting layer and a hole transporting layeror two layers as using a material which supports both a light-emittinglayer and an electron transporting layer and a hole transporting layer.

For a red light emitting material, for instance, we can usetriphenyldiamine derivative TPD(N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine) orα-NPD (4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl) and DCM-1(4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4-H-pyran)distributed Alq3 (tris(8-quinolinolate)aluminum) for the electrontransporting light-emitting layer (dual usage for an electrontransporting layer and a light emitting layer).

For green light emitting material, for instance, we can usetriphenyldiamine derivative TPD or α-NPD for hole transporting layer andAlq3 or quinacridon-doped Alq3 or Bebq (bis(8-hydroxyquinolinate)beryllium) for the electron transporting light-emittinglayer (dual usage for an electron transporting layer and a lightemitting layer).

For blue light emitting material, for instance, triphenyldiaminederivative TPD, α-NPD for the hole transporting layer and DPVBi(4,4′-bis(2,2-diphenylvinyl)biphenyl) or a material consisting of DPVBiand BCzVBi (4,4′-bis(2-carbazolevinylene)biphenyl) or a material dopedwith distyrylallylene derivative as a host and distyrylamine derivativeas a guest for the light emitting layer and Alq3 for the electrontransporting layer. We can use Zn (oxz)2(2-(O-hydroxyphenyl)-benzoxazole zinc complex) for the electrontransporting light emitting layer (dual usage for an electrontransporting layer and a light emitting layer).

Moreover, we can use materials of polymer system in stead of the abovematerial of a low molecular-weight system. As for the polymer basematerials, we can use multiple-layer film of PEDT/PSS (a mixed layer ofPolyethylene dioxy thiophene and Polystyrene sulphonate) and PPV(poly(p-phenylene vinylen)) for the hole transporting layer and thelight emitting layer. Also we can use green ink blended PPV for greencolor light emission, rhodamine 101 blended green ink as a dopant forred-color light emission and F8 (Poly (dioctylfluorene)) for a bluecolor light emitting layer. In addition, F8 can function as an electrontransporting layer. We can use dye containing polymer such as PVK(poly(N-vinylcarbazole)). Each layer of the multiple layer film is inthe order of several tens of nano meters which is less than the wavelength of the light.

As for the pattering of the organic layer 100 in each predeterminedposition for each picture element in a fashion of an island, we can usea published technology as pattered-film forming technology used fordeposited organic layer through shadow masks (for instance, S.Miyaguchi, et al.: “Organic LED Fullcolor Passive-matrix display”,Journal of the SID, 7, 3, pp 221-226 (1999)). In this process, the bank500 can be used as a spacer of the shadow masks. When the organic layer100 is composed by a material of a polymer system, we can use publishedink-jet technology (for example, T. Shimoda, et al.: “Multicolor PixelPatterning of Light-Emitting Polymers by Ink-Jet Printing”, SID 99DIGEST, 376 (1999)). In this process, the bank 500 functions as a torusisolating the picture element area.

A tilted reflective surface 700 is formed on the surface of the slope ofthe bank 500, which must be on the transparent electrode 200. The tiltedreflective surface 700 is formed by high reflective metal such asaluminum, silver or chrome in the process of deposition through masks orin the photolithographic patterning processing. In addition, thefollowing effect can be obtained when the tilted reflective surface iscomposed by a metal film. In general, the transparent electrode hashigher electrical resistivity than a metal electrode. Therefore, thedisplay device which has a large display size tends to have the voltagedifference due to the electrical resistivity between the location closeto the power supply and that far to it. Due to this voltage difference,the electric current flowing into the OLEDs composing the pictureelement differs among those close to the power supply and far from it,that results in the lack of uniformity in the intensity of emittedlight. For this problem, by forming the tilted reflective electrodesmade of a metal that directly contacts to the transparent electrodes,the tilted reflective electrodes works as low resistive electrodesarranged thereon like as a meshed formation and the effect to suppresssuch lack of uniformity can be obtained.

For the tilted reflective surface 700, a multiple layered film usingtransparent dielectrics material such as silicon oxide, silicon nitrideor titanium oxide may be formed for the reflective surface. For thiscase, we obtain a feature of loss less reflective surface against thelight reflection but drawbacks as longer manufacturing process and thereflectivity dependence against the wavelength and the tilt angle thatare subject to the issues to be studied. In the flat surface surroundedby the tilted reflective surface 700, an optical waveguide layer 600 isformed with a transparent material. The optical waveguide layer 600should be made of lower refractive material than that of the transparentelectrode 200. For this case, after liquid-repellent process to thetilted reflective surface 700 corresponding to the space between twopicture elements, the optical waveguide layer 600 is formed by afilm-forming of the material consisting of binder resin and solvent bymeans of spin coating, blade-coating, etc. and finish-processing in drysolidification. A selective film-forming by using ink-jet printingtechnology for such a flat surface 25 surrounded by the tiltedreflective surface 700 can be used before the dry solidification.

The binder resin that composes the optical waveguide layer 600 is notnecessary to be self-polymerizing but merely dry-solidified orpolymerize-solidified after film coating. For this last material, higherdurability and tighter contact than that for dry solidification.However, since polymerize-solidification needs UV light or X rayexposing or thermal heating, it is necessary to select the least damageprocess against the organic layer. For the optical waveguide layer 600,one of resins or mixed with the plurality of them as transparent acrylicresin, benzocyclobutene resin, polyimide resin, epoxy resin, polyacrylamide resin, polyvinyl alcohol, etc. or photoresist is usable. It isimportant to keep the height H2 of the optical waveguide layer 600 beless than the height H1 after solidification of the optical waveguidelayer from the previous reason.

On the optical waveguide layer 600, a seal-off material 900 is set viathe gap 950. For the seal-off material 900, a glass plate, plastic filmswhich are enhanced for gas-barrier characteristics using inorganiclayers, complex layered material using thin glass plates and plasticfilms. The seal-off material can keep a gap 950 against the opticalwaveguide layer 600 with using the bank 500 as a spacer and is fixedwith the substrate 800 by adhesive seal material formed around theperipheral of the display portion 2 in a form of a frame. For thisfixing, a gap 950 is filled with inert gases as nitrogen and kept assealed-off by cementing the seal-off material 900 to the substrate 800in air tight manner. In addition, desiccant is preferable to be putbetween the seal-off material 900 and the substrate 800 on necessitywithout degrading the display capability.

Next, we explain the display operation of the display device 1 usingFIG. 8, FIG. 11 and FIG. 12. FIG. 11 is a timing chart of the voltageVG1, VG2, . . . , VGm applied to the gate line G1, G2, . . . , Gm inorder. FIG. 12 shows the voltage status of the gate voltage VG1, thedata voltage VD1 and the voltage of the storage capacitor 23. As shownin FIG. 11, to the lines G1, G2, . . . , Gm, the VG1, VG2, . . . , VGmthat turn-on the switching transistor 21 are applied to the gate lineG1, G2, . . . , Gm in order. When the VG1, which turns on the switchingtransistor 21, is applied to the gate line G1 at the time t=t₀, the nextturn-on voltage, after one vertical sweep of scanning with one frameterm Tf, is applied to the gate line G1 at the time t=t₀+Tf. For thisdriving scheme, the time duration to apply the turn-on voltage to theone gate line is less than Tf/m. In general the time duration as 1/60second is used for Tf time value.

Once a turn-on voltage is applied to a gate line, all transistors, thatare connected to the gate line turn into turn-on status and asynchronous data voltages responding to picture signals are applied tothe data lines. This is called as progressive line scanning method.Focusing to the picture element locating at the cross point of the firstcolumn and the first row, we explain the gate voltage VG1, the datavoltage VD1 and the voltage status of the storage capacitor 23 withreference to FIG. 12. We assume the value d1 for the data voltage VD1which is in synchronous to VG1 and the value d2 for the data voltage atthe time of the next frame t=t₀+Tf. In this case, these data voltagesare stored in the storage capacitor 23 while the turn-on voltage isbeing applied to the gate line G1 and these voltages are kept in aboutvalues for one frame term. These voltages determine the gate voltage ofthe driver transistor 22 and the current though the transistor iscontrolled by the gate voltage. The voltage and that given by these andcommon voltage line and the voltage Va applied to the transparentelectrode determines a electric current which flows into thelight-emitting element.

In other words, in synchronous to the turn-on voltage applied to thegate lines corresponding to the picture elements of which lightintensity should be controlled, it is possible to control the lightemission of the picture element by applying the voltage corresponding tothe image information through the data lines. Therefore, it is possibleto present a predetermined image by controlling the light emission fromthe plural picture elements that compose the display portion 2.Moreover, the response time of starting light emission after applyingthe voltage between the cathode and anode of the light-emitting elementis generally less than 1 μs, therefore it is possible to display thepicture image which is high-speed moving picture. Intense light emissionis generally obtained for bright picture presentation by large currentthat flows through the organic light emitting diode but electric powerconsumption becomes large and life time of the diode (for example,defined as the life at the half intensity as the initial one) becomesshorter as au increasing of the current.

As described above, the present invention can use the light as the imagelight with good efficiency although the light is lost in the propagationfor the past conventional technology. Therefore, the display devicesthat have more intensity of light, emission and the brighter picturepresentation than those in the conventional technologies. The lowerpower consumption due to less current flowing into the light-emittingelement and longer life time can be realized for the same intensity oflight in a display device. Moreover in the display device according tothe present invention, the optical waveguide layer is separated for eachpicture element, no picture degrading such as optical cross talk or blurof presentation due to no light is guided to other picture element,resulting into a display with clear images and high quality images.

Moreover, we have presented an embodiment wherein the light emittingarea is on the flat plane of the substrate and has no step differencesdue to the presence of the driving devices or wiring lines thereon andwherein the step differences due to the driving devices and wiring linesare covered by the banks, however the embodiments are not confined insuch configuration. For example, on the substrate on which the drivingdevices and the wiring lines are formed, all of the display portionincluding the step differences due to the driving device and wiringlines is covered by a planarizing layer consisting of an insulatingmaterial, on which flat surface those constructing elements of thisinvention as the reflective electrodes and banks or the like can beformed. For an organic planarizing layer material as acryl base resin,benzocyclobutene resin or polyimide base resign can be used. By the filmforming method using spin-coating of these materials, the surface ofthese films can be easily flattened. By utilizing the surface on thewiring lines and driving devices after film forming by planarizing layersuch as the light emitting area, then we can obtain extensive lightemitting area even though we have no sufficient area for the flat areadue to relatively large area necessary for wiring lines and drivingdevices against the physical size of the picture elements therefore wecan realize bright display device.

In the above embodiment, we have explained the active matrix drivescheme, however this invention is not limited in this specificembodiment. For example, we can apply the present invention to a passivematrix driving display device where the electrodes are directlyconnected to the vertical scanning lines and horizontal scanning lines.Moreover the arrangement of picture elements can be either of a stripearrangement, a mosaic arrangement or a delta arrangement and we canselect an appropriate arrangement to be compliant to the requirementspecifications of the display devices.

Next, we explain the manufacturing method of the first embodiment ofthis invention referring to FIGS. 13A-13D to FIGS. 16A-16C. FIGS.13A-13D show the process to manufacture the banks in this manufacturingmethod of the display device according to the present invention. Asshown in FIG. 13A, driving devices (such as thin film transistors,hereinafter) and wiring lines are formed on the substrate 800 and on topof the substrate an insulating layer 890 is formed and electrode layer310 to be used for the reflective electrode 300 consisting of aluminum,magnesium, magnesium-silver alloy or aluminum-lithium alloy is formed.It should be noted that thin film transistors and wiring lines areomitted in the drawings. The electrode 310 for the reflective electrode300 is electrically connected to the thin film transistors for drivers.Next, we coat the photoresist on the electrode layer 310 for thereflective electrode 300 and make patterns of photoresist by means ofphoto-lithography. We etch the electrode layer 310 by using the patternsof the photoresist and obtain the island-shaped reflective electrode 300corresponding to the picture element, as shown in FIG. 13B afterremoving unnecessary photoresist.

Next, we coat the photoresist in a certain predetermined thickness byspin-coating over on the substrate 800 on which the reflective electrode300 has been formed. The thickness of the photoresist can be controlledby the viscosity by adjusting density of the resist since it is solvedin a solvent and further controlled by the spinning rotation speed ofthe substrate in the film forming process. After coating thephotoresist, photoresist film 510 is formed by heating and evaporatingthe solvent. The photoresist film 510 is exposed to the light throughphoto masks 810 (FIG. 13C) and is developed into the shape of banks 500between the picture elements as shown in FIG. 13D. There are two kindsof photoresists; as negative one and positive one. Since nolight-exposed portion is solved in the development for the negative typeresist, the cross sectional shape of the photoresist tends to berectangular or close to trapezoid. For the positive type resist, thecross sectional shape of the resist after development tends that theside surface of the resist is decreasing in accordance with the locationof the side surface apart from the surface of the substrate. Theselection should be done by considering the features such that theshapes closer to the desired ones are obtained.

For the negative type resist, we can use cinnamic acid base resist orrubber base resist as cyclized rubber added with bisazide compound forphotosensitive radical. For the positive type resist, we can use a mixedmaterial of naphtoquinonediazido compound for photosensitive agent andalkali-soluble phenolic resin. A concrete example of the positive typeresist, there is a commercial product call “OPTOMER PC” (manufactured byJSR Corporation). This resist is a mixture of acryl base resin andnaphtoquinonediazido compound. The viscosity is, for example for the useof “OPTOMER PC403”, controlled as 3.5 μm thick film is formed when it iscoated in the spinning speed of 700 rpm.

For this case, we coat the photoresist on the substrate, dry by thermalheath and photo-expose by using a photo mask so that the areas of thebanks are exposed. By these processes as exposure, development andheating, we obtain the bank 500 in a cross sectional shape as exampledin FIG. 14. The tilt angle β of the side surfaces of the bank at thenearest to the substrate surface is from 30° to 60° depending upon theprocess condition and it continuously decreases according to being apartfrom the substrate surface. For example, we obtain the angle β about 60°and the tilt angle is 20° at the height of 3 μm for the bank that has3.5 μm height. This bank can be used for this embodiment. We can usephotosensitive polyimide as a positive type photoresist product of whichcode is HD8010XF2 (Hitachi Chemical Co. Ltd.).

As for the photo mask 810, we use ultra-violet light-transmissive fusedsilica substrate on which shadow pattern is formed by the metal film. Wecan use a photo mask that has light control capability by controllingthe thickness of the shadow metal or the area of the plural small openhole at the location of the shadow masks that are effective to thetransparency change in continuous, manner. We have discussed the processto use photoresist for making the banks because we can manufacture thebanks of several micron meters height in a practical processing time.

However this invention does not exclude inorganic material as siliconoxide or silicon nitride for the use of banks. For the case of usingsilicon nitride, we can form the bank by the silicon nitride layerformed by CVD (Chemical Vapor Deposition) on the substrate and patternedby etching through the resist pattern made photo-lithography technologyand removing the unnecessary photoresist thereon. By varying the densityconditions of the NH3 and SiH4 supplied for the film forming process, wecan control the shape of the tilted surface, of the bank after etchingdue to multiple layers of silicon nitride with different filmproperties. Any forming method, for example screen printing method ordirect drawing of the ink-jet, is exploited to form the bank 500 as faras the required tiled surfaces are obtained.

FIGS. 15A-15C show the process to manufacture the organic layer portionof the display device according to the present invention. We make thebank 500 in the previously described process, and then we form theorganic layer 100 on the part of the tilted surface of the bank 500 andon the reflective electrode 300 in the area surrounded by the bank 500.As shown in FIG. 15A, the forming of the organic layer 100 is done bydepositing the organic material via a metal mask which has the openareas corresponding to the locations of the light emitting areas. Forthis case, the bank can be used as a spacer to suspend the mask. For thecase when the organic layer is polymer type, the film forming is done byblowing the solution of solvent and the organic material from theink-jet head 830 using the control method with a piezo device, asso-called ink-jet patterning technology as shown in FIG. 15B. For thismethod, the banks 500 can work as dams to store the ink-droplet.

After forming the organic layer, the transparent electrode 200 is formedon all of the display portions. For the transparent electrode,electrically conductive transparent film as ITO or IZO can be used andit is formed by vacuum evaporation or sputtering process (see FIG. 15C).However, it is difficult to form low resistive transparent film by usingthe conventional deposition method and damages are made in the organiclayer 100 resulting into degradation of the characteristics in the caseof using sputtering method. Therefore an ion plating device or a countertarget sputtering device, wherein plasma does not directly contact ontothe surface of the substrate, is better to be used in forming thetransparent electrode 200 in order to makes less damage as possible. Wecan form a thin metal deposition film through which the light transmitsdirectly onto the organic layer before forming the transparentconductive film. We may exploit the transparent conductive filmdeposited on this thin metal deposition film for the transparentelectrode. For this case, the thin metal deposition film works as ablocking layer, it is possible to reduce the damage onto the organiclayer when the transparent conductive film. For this blocking layer, wecan use the metal as gold, platinum or chrome that has a high workfunction in the thickness of about 10 nm.

FIGS. 16A-16C show the process to manufacture the optical waveguidelayer of the display device according to the present invention. As shownin FIG. 16A, we form the tilted reflective surface 700 by selectivelydeposited high reflective metal such as aluminum using a metal mask thathas the open holes corresponding to the banks 500 made in the processdescribed above. Afterwards, we blow the compound material for theoptical waveguide layer to the basin area surrounded by the bank 500through the ink-jet head 850 as shown in FIG. 16B. The compound materialconsists of solvent and the binder resin which is transparent forvisible light. We form the optical waveguide layer 600 which is slightlylower than the top end of the tilted reflective surface as shown in FIG.16C in such a way that the compound material of the optical waveguidelayer is stacked up to the height similar to that of the bank orslightly low than that of the bank, is kept for a mean time enough toget wet with the transparent electrode 200 and the tilted reflectivesurface 700 and to obtain leveling and then dried and solidified. We mayform the predetermined optical waveguide layer by repeating to blow thecompound material for the optical waveguide layer, dry and solidify.

For the binder resin to compose the optical waveguide layer 600, abinder resin that has no polymerization property but is merely dried forsolidification is usable and another binder resin that is solidified bya polymerizing process after film forming is usable, as well. The resinthat can be solidified by polymerizing process has tighter contact andhigher durability than the simple dry and hardening process, however itneeds an optimization of the process for, exposing to ultraviolet lightor electron beam or that for heating in order to obtain the least damageto the organic layer.

We can use a resin or a complex mixture of resins from acrylic resin,benzocyclobutene resin, polyimide resin, epoxy resin, polyacryl amideresin, polyvinyl alcohol, etc. By using such material for the opticalwaveguide layer 600, it is possible to make an optical waveguide layerthat has smaller refractive index than such transparent electrodes asITO and IZO and larger one than the air.

As for forming the optical waveguide layer, the film forming of theoptical waveguide layer compound material is done by coating over thesubstrate using a spin-coater drying for hardening besides selectivelydepositing the compound in the area of the basin surrounded by the banksby using ink-jet. In this case, the substrate is exposed to O2 plasmaand then CF4 plasma after forming the tilted reflective surface butbefore forming the layer of the optical waveguide layer compoundmaterial. In this case, the tilted reflective surface made of aluminumwhich is only fluorinated has liquid-repellency and the transparentelectrode which is not fluorinated keeps wettable surfacecharacteristics to the optical waveguide layer compound material.Therefore the optical waveguide layer compound material stays on thearea to which the transparent electrode surface expose and not on thetilted reflective surface. This results in the optical waveguide layersisolated by the tilted reflective surface for each of the pictureelement.

It is desirable that the optical waveguide layer is completely isolatedby the tilted reflective surface, however each the isolated waveguidelayer it connects to that on the adjacent picture element beyond thetilted reflective surface. For this case, in the area where the opticalwaveguide layer is thinnest, mostly at the ridgeline of the bank, thethickness of the optical waveguide layer is less than the visible lightwavelength and waveguide modes are so limited that only little amount oflights leaks to the next picture element. Therefore, even though theoptical waveguide layer has continuity to that in the area of theadjacent picture elements, the optical waveguide layer is practicallyisolated provided the thinnest optical waveguide layer is less than thevisible light wave length. Therefore this invention does not necessarilyexclude such continuity of the optical waveguide layer.

As shown in FIG. 1, the seal-off material is fixed with the substrate800 with adhesive sealing cement formed in a frame shape around theperipheral area of the display portion by keeping the gap 950 betweenthe seal-off material 900 and the optical waveguide layer 600 with thebank 500 as a spacer. The gap 950 has an equivalent refractive index tothe air by filling the inert gas as nitrogen with the gap 950 betweenthe seal-off material 900 and the substrate 800. As for the seal-offmaterial 900, we can use that of transparent for visible light andgas-barrier capable plates such as a glass plate, a plastic filmprocessed for gas barrier, a multi-layer with glass plates and theplastic films.

The Second Embodiment

Next, we will explain another embodiment of the display device regardingto this invention. FIG. 17 shows across sectional view of anotherembodiment of the display device. In this display device, the height H3of the optical waveguide layer locating at the central area of the basinarea surrounded by the bank 500 is continuously larger as being closerto the bank 500. Besides the height H4 of the optical waveguide layer600 on the tilted reflective surface 700 is larger than H3, we will usethe same signs and notations for the same portions and omit the detailedexplanation.

For the optical waveguide layer 600 which satisfies the relation ofthese heights, we can form it by controlling the dry out speed of thecoated optical waveguide layer compound material when we coat theoptical waveguide layer compound consisting of binder resin and solventwith taking the boiling point and the vapor pressure of the solvent inthe room temperature into account. In other words, we can obtain theoptical waveguide layer in a form that the height is low in the centralarea surrounded by the bank and is high on the tilted reflective surface700, in accordance with the volume shrinkage after coating the opticalwaveguide layer compound, leveling the coated film and drying forsolvent evaporation. In this case, the surface of the optical waveguidelayer 600 is not parallel but declines to the surface of the substrate.

Next, we will explain the effect of the optical waveguide layer 600described above. FIG. 18 and FIG. 19 show the cases of the opticalwaveguide layer 600 has the different height for each location, that is,the surface of the optical waveguide layer 600 is not parallel to thesubstrate. FIG. 18 shows the case where the height of the opticalwaveguide layer on the upper location of the light 2100 which isemitting the light at location 190 is lower than the height of the layerat the location 690 where the light 2100 reflects on the surface of theoptical waveguide layer. We assume the incident angle and reflectionangle of the light 2100 at the surface of the optical waveguide layeragainst the surface parallel to the substrate as θ3 and θ4,respectively. Then the relation θ3>θ4 is satisfied, the light reflectedon the surface of the optical waveguide layer is more parallel to thesubstrate. Therefore, the times of reflecting on the reflectiveelectrode 300 until the light traveling until reaching to the tiltedreflective surface in the optical waveguide layer decrease and the lightloss by absorbing the light at the reflective electrode, that resultsinto improving the external coupling efficiency.

On the other hand, FIG. 19 shows the case where the height of theoptical waveguide layer on the upper location of the light 2100 which isemitting the light at location 190 is higher than the height of thelayer at the location 690 where the light 2100 reflects on the surfaceof the optical waveguide layer. We assume the incident angle andreflection angle of the light 2100 which is totally reflected at thesurface of the optical waveguide layer against the surface parallel tothe substrate as θ3 and θ4, respectively. Then the relation θ3<θ4 issatisfied, the light reflected on the surface of the optical waveguidelayer is more vertical to the substrate. Therefore, the totallyreflected light on the optical waveguide layer surface at the first timehas the smaller incident angle when the light again incidents to thesurface of the optical waveguide layer. If the incident angle is smallerthan the critical angle, then the light comes out to an outer viewerbefore the light comes up to the tilted reflective surface. Thereforewhen the outer surface of the optical waveguide layer tilts to thesubstrate, higher external coupling efficiency is obtained than in thecase where the optical waveguide layer is parallel to the substrate.

The Third Embodiment

Next, we will further explain another embodiment of the display deviceregarding to this invention. FIG. 20 shows a cross sectional view of apicture element in this another embodiment. For this embodiment of thedisplay device, the thickness of the optical waveguide layer has themaximum at the center of the area surrounded by the bank 500 and iscontinuously less as being closer to the bank. Since the fundamentalconstruction is same as the embodiment described above besides the shapeof the optical waveguide layer is convex, we mark with the same signsand notations to the same portions and avoid the explanation. This shapeof the optical waveguide layer is made by making the tilted reflectivesurface 700 liquid-repellent and the transparent electrode 200 exposingto the optical waveguide layer liquid-wettable before coating theoptical waveguide layer compound material consisting of binder resin andsolvent. As a concrete process, the substrate is exposed to oxygenplasma and CF4 plasma in order before coating the optical waveguidelayer compound material.

In this case, if the tilted reflective surface is made of aluminum thenthe surface is fluorinated and has liquid (water)-repellentcharacteristics, however the transparent electrode is not fluorinatedand keeps wettable surface characteristics against the optical waveguidelayer compound material. In stead of these processes, we can make thetilted reflective surface liquid-repellent and the transparent electrodeexposing to the optical waveguide layer selectively liquid-wettable bycoating all over the substrate with a transparent wettability-convertedlayer which is not shown in the figures. The wettability-converted layercan be formed by coating a solution in which the binder resign, thephotocatalyst and the necessary additives are dispersed, drying andfixing the photocatalyst in the hardened resin. If the thickness of thewettability-converted layer is large, then it allows guiding the lightand causes the optical cross-talk by light leak to other pictureelements. Therefore it is desirable that the particle size of thephotocatalyst should be less than 10 nm and the layer being less than300 nm. We can exploit titanium oxide for the photocatalyst andorganosiloxane polymer for the binder resin. After forming thewettability-converted layer and photo-exposing with the tiltedreflective surface blocked off from the exposure and the transparentelectrode exposing to the optical waveguide layer through the photomask, the exposed wettability-converted layer turns to be highliquid-wettability and the non-exposed one maintains to beliquid-repellent.

After making the tilted reflective surface 700 liquid-repellent and thetransparent electrode 200 exposing to the optical waveguide layerliquid-wettability, the coated optical waveguide layer compound materialturns into a convex shaped optical waveguide layer such that thethickness of the optical waveguide layer is the maximum at the center ofthe area surrounded by the bank and is continuously decreasing inclosing to the bank 500. For this construction, improvement of theexternal coupling efficiency can be expected due to the slope of theoptical waveguide layer 600 against the substrate surface.

The Fourth Embodiment

Next, we further explain another embodiment of the display deviceregarding to this invention. FIG. 21 shows the cross sectional view of apicture element that explains another embodiment. This embodiment has anincreased optical waveguide layer and the maximum height of the layer ishigher than the height of the bank therefore the fundamentalconstruction is same as the embodiment described above. From thisreason, we use the same signs and notations for the same portions andomit detailed explanations. In this embodiment, it is possible to makeonly the ridgeline of the bank liquid-repellent and the other partsincluding the tilted reflective surfaces selectively highliquid-wettable by blocking the light exposure onto the ridgeline of thebank when the light is exposed onto the wettability-converted layer. Inthis embodiment, improvement of the external coupling efficiency can beexpected due to the slope of the optical waveguide layer 600 against thesubstrate surface. In addition, a display device that has high intensityof the light emission normal to the front surface is realized due to thefocusing effect of the optical waveguide layer as the convex surfaceshape of the optical waveguide layer. However, the bank 500 cannot beused as a spacer between the substrate 800 and seal-off material whenthey are tightly cemented. Therefore, we can use an adhesive sealmaterial including beads or small rods pasted at the peripheral area ofthe display portion in a shape of a frame to such area and then thesubstrate 800 and the seal-off material 900 are fixed in nitrogen gasfilled therebetween.

The Fifth Embodiment

Next, we explain another embodiment of the display device regarding tothis invention. FIG. 22 shows a cross sectional view of the pictureelement of the display device regarding to this invention. Thisembodiment is the one wherein a modification is applied to theembodiment explained in FIG. 1 such that the seal-off material 900 isreplaced by an optical waveguide layer 650 (called a gas-barrieringoptical waveguide layer, hereinafter) that is transparent and high denseand has high gas-barriering characteristics and that is further formedon the optical waveguide layer 600. Since the other constructions aresame as the above embodiment, we use the same signs and notations forthe same portions and omit detailed explanations. For the gas-barrieringoptical waveguide layer, we can use silicon nitride, titanium oxide andwe optimize the condition such as the gas flow rate in case of usingchemical vapor deposition method by which we obtain dense film formingas possible. We form a multi-layered gas-barriering layer in stead of asingle layer and moreover we optically isolate the layer on each of thepicture elements by using photo-lithography technology on necessity.Being same as the above embodiment, the external coupling efficiency isimproved and the display device that presents a distinct picture qualityand has no optical cross talk, is realized. Especially, there is a meritthat a thin and light display device is realized since no seal-offmaterial is used.

The Sixth Embodiment

Next, we explain another embodiment of the display device regarding tothis invention. FIG. 23 shows a cross sectional view of the pictureelement of the display device regarding to this invention. Thisembodiment is the one wherein a modification is applied to theembodiment explained in FIG. 1 such that a tilted reflective surface700, which has a reflective electrode function as well, is formed on thereflective electrode 300 and the slope surface of the bank 500 beforeforming the organic layer 100 and the organic layer 100, transparentelectrode 200 and the optical waveguide layer 600 are formed thereon.Since the other constructions are same as the above embodiment, we usethe same signs and notations for the same portions and omit detailedexplanations. We explain the fabrication process of the embodiment shownin FIG. 23 in referring to FIGS. 24A-24C, FIGS. 25A-25C and the drawingof the previous embodiment. FIGS. 24A-24C and FIGS. 25A-25C are processdrawings that explain the manufacturing method of another embodimentshown FIG. 23 regarding to this invention.

The process for this embodiment is same as the previous embodiment up tothe step wherein driver elements and wiring lines are formed and theisland-shaped reflective electrode 300 consisting of aluminum,magnesium, magnesium-silver alloy or aluminum-lithium alloy and banks500, that correspond to the picture element, are constructed on asubstrate 800 with an insulating layer 890 on the upper surface. In thenext step, we form a layer consisting of reflective metal materialsimilar to the reflective electrode 300 over all surface of the displayportion and then we construct the island-shaped tilted reflectivesurface 700, that corresponds to the picture element, on the reflectiveelectrode 300 and the slope surface of the bank 500 by applyingphotolithography technology and etching as shown in FIG. 24A. Therefore,the tilted reflective surface 700 and the reflective electrode 300 areelectrically connected and then the tilted reflective surface 700 worksas a reflective electrode.

In the next step, as similar to the above embodiment explained by usingFIGS. 15A-15C, the organic layer 100 is formed by selective depositionthrough masks or selective ink-jet patterning. In this case, the organiclayer 100 is necessary to be formed in an extensive area so that itcompletely covers the edges of the tilted reflective surface 700 (asshown in FIG. 24B). Because a failure is caused by the electricalshortage between the tilted reflective surface and the transparentelectrode 200 formed on the organic layer 100 if the edge of the tiltedreflective surface is unconcealed.

In the next step, the transparent electrode 200 is formed all over thedisplay portion as shown in FIG. 24C. We can use ITO or IZO for thetransparent electrode as described in the above embodiment and we canform it in the same method used for such embodiment. As further in FIG.25A, we coat the wettability-converted layer on necessity all over thedisplay portion. The wettability-converted layer is the layer for whichwe can change the wettability of a selectively predetermined area asliquid-repellant to liquid-wettable or vis-a-vis. We can use a filmconsisting of photocatalyst and binder resin. For this case, thewettability-converted layer can be formed by coating a solution in whichthe binder resign, the photocatalyst and the necessary additives aredispersed on solvent, drying and fixing the photocatalyst in thehardened resin. If the thickness of the wettability-converted layer islarge, then it allows guiding the light and causes the opticalcross-talk by light leak to other picture elements. Therefore it isdesirable that the particle size of the photocatalyst should be lessthan 10 nm and the layer be less than 300 nm. We can exploit titaniumoxide for the photocatalyst and organosiloxane polymer for the binderresin. After forming the wettability-converted layer and photo-exposingthrough a photo mask 870, the exposed wettability-converted layer turnsto be high liquid-wettability and the non-exposed one maintains to beliquid-repellent.

Therefore, the ridgeline of the bank 500 corresponding to the isolationgap between the picture elements maintain liquid-repellency and theother portion turns to be highly liquid-wettable after light-exposing tothe wettability-converted layer through a photo mask 870 which blocksthe light for the ridgeline of the bank 500 corresponding to suchisolation gap and lets the light transmitting to other portions (asshown in FIG. 25B). In the next step, the optical waveguide layercompound material 680 is blown onto the basin area surrounded by thebank 500 from the ink-jet head 880 as shown in FIG. 25C. As same as theabove embodiment explained in reference to FIG. 16, the opticalwaveguide layer compound material at least consists of solvent andbinder resin which is transparent to the visible light. The opticalwaveguide layer compound material is stacked up to the level similar tothe height of the tilted reflective surface 700. In this case, the blownoptical waveguide layer does not stay on the ridgeline of the bank 500and to moves to a puddle in the basin area surrounded by the bank 500.After we keep the blown optical waveguide layer compound material toobtain enough leveling, then we form the optical waveguide layer 600which is optically isolated on each picture element by making the levellower than the upper edge of the tilted reflective surface 700 after dryand solidification. In addition, we can form the desired construction ofthe optical waveguide layer not only by a single process of blowing theoptical waveguide layer compound material, drying and solidifying but byrepeating such process.

As the next step, we fix the seal-off material 900 with the substrate800 by adhesive seal material formed around the peripheral of thedisplay portion in a form of a frame in a status that a gap 950 betweenseal-off material 900 and the optical waveguide layer 600 is kept by thebank 500 as a spacer. The gap 950 has an equivalent refractive index tothe air by filling the inert gas as nitrogen between the seal-offmaterial 900 and the substrate 800. In this embodiment, as same as theabove embodiments, being different to the conventional technologywherein the light propagate in parallel to the substrate and then islost in decay, the light is guided by the optical waveguide layer 600 tothe tilted reflective surface 700 and then change the direction of thepropagation by the reflection at the tilted reflective surface 700 andis used as an effective display image light to the viewer resulting intothe improvement of the external coupling efficiency. Since the opticalwaveguide layer 600 is completely isolated, the light emitted from anorganic layer of a certain picture element does not, propagate in otherdifferent picture elements and no picture quality problem as opticalcross-talk or blur of presentation occurs, that results in realizing adisplay device that has high quality picture image. Moreover, in thisembodiment, the tilted reflective surface 700 does not only work as areflection surface but reflective electrode of OLED consisting of thereflection electrode, the organic layer 100 and transparent electrode200. Therefore, the slope surface of bank 500 is used for the emissionarea as well as the flat surface 25 therefore the relatively extensiveemission area in comparison to the embodiment shown in FIG. 1 is usedand brighter display device is obtained on the basis of the same size ofpicture element.

FIG. 26 shows a cross-sectional view of the display device of anembodiment of this invention. The reflective electrode 300 electricallyconnects with the driver element on the area covered by the bank 500 assame as in the above embodiment. In other words, the electrode 26 of thedriver transistor and the reflective electrode 300 is connected throughthe contact hole 31 made in the insulation layer 30. The contact hole 31locates underneath the bank 500 and the tilted reflective surface 700.This implies that the contact hole area which cannot be used as a lightemitting one is kept under the tilted reflective surface and the otherarea that emits the light is obtained as the light emitting area. Thisconstruction is efficient for realizing highly intense of the lightemission.

The Seventh Embodiment

Next, we explain another embodiment of this invention. FIG. 27 shows aplanar view of the display device of an embodiment of this invention. Aunit picture element is shown as one of additive primary colors given bya red-color emission pixel, a green-color emission one and blue-coloremission one therein. The pixel in this embodiment is constructed as thepicture element 20 of the display device explained in referring to FIG.1 and FIG. 2 is separated by the tilted reflective surface 700 and thebank 500 into a plurality of the areas for each of such pixel. Since theother constructions are same as the above embodiment, we use the samesigns and notations for the same portions and omit detailedexplanations.

In the display device for this embodiment, a picture element issegregated into a plurality of light emitting areas and we can controlthe viewing angle characteristics of the device by changing the relationbetween the size of the area and the height of the optical waveguidelayer 600. This is, as described above, from the fact that the height ofthe tilted reflective surface and the thickness of the optical waveguidelayer 600 against the size of the light emitting area influence to theexternal coupling efficiency. In other words, the longer the width ofthe light emitting area against a certain height of the tiltedreflective surface and a certain thickness of the optical waveguidelayer is formed, then the smaller the external coupling efficiency andreversely the shorter the width of the light emitting area, the largerthe external coupling efficiency and the wider viewing angle areobtained. For the case of the above embodiment explained in referring toFIG. 2, the viewing angle for the horizontal orientation becomes largerthan that of vertical orientation against the drawing plane. On theother hand, the display device that has same viewing anglecharacteristics for vertical orientation and horizontal orientation isrealized by segregating the light emitting area of a picture elementinto a plurality of light emitting areas and making the length H3 in thevertical orientation same as the length W2 in the horizontalorientation. Especially in this invention, the external couplingefficiency can be larger, regardless to the size of the pictureelements, than that in the case of using non-segregated picture elementby segregating the picture element into a plurality of light emittingareas since we can shorten the width of the light emitting area againstthe height of the tilted reflective surface and the thickness of theoptical waveguide layer. Therefore, a brighter display device isrealized in comparison to other ones which consume the same electricpower.

FIG. 28 shows the cutaway view along the line C-C of an embodiment shownin FIG. 27. A picture element in this embodiment is segregated into aplurality of areas by the bank 500 as described above. In order tosuppress the increase of the defective fraction due to the increase ofquantity of the driver elements, these segregated areas corresponding toa picture element are driven by a pair of driver elements of whichconfiguration does not complicate the circuitry. For this purpose, thereflective electrode 20 is not segregated and a single island-shapedreflective electrode 300 is made for a single picture element 20.Therefore, the bank 500 that segregates the picture element into aplurality of areas is formed on the reflective surface 300 as shown inFIG. 28. For this case, since the reflective electrode 300 connects toother portion of the electrode on the flat surface under the bank 500,therefore no failure due to the break by the step difference occurs.Moreover, the transparent electrode 200 is hard to be broken at theridge of the bank 500 since the tilted reflective surface 700 that worksas an electrode is stacked on the transparent electrode.

FIG. 29 shows the cutaway view along the line C-C for an embodimentshown in FIG. 27 for the case of the embodiment shown in FIG. 23. Forthis case, the reflective electrode is not segregated, a singleisland-shaped reflective electrode 300 is made for a single pictureelement 20 and the bank 500 that segregates the picture element into aplurality of areas is formed on the reflective electrode 300 as shown inFIG. 29. Therefore no breaking of electrode occurs due to the stepdifference by the bank 500 since the reflective electrode 300 connectsother portions of the electrodes on the flat surface. Moreover, theshape of the pixels segregated from a picture element can be any one asa polygon as a triangle and a hexagon, an ellipsoid or a circle as faras we can obtain the desired viewing angle characteristics.

The Eighth Embodiment

Next, we will explain another embodiment of this invention. FIG. 30shows a cross sectional view of a picture element explaining anotherembodiment of the display device according to the present invention.This embodiment is the display device wherein a modification is appliedto the embodiment explained in FIG. 23 such that the reflectiveelectrode is eliminated and the tilted reflective surface 700 shown inFIG. 23 is replaced by the reflective electrode 350 that functions asthe tilted reflective surface 700 shown in FIG. 30 as well. Since theother constructions are same as the above embodiment, we use the samesigns and notations for the same portions and omit detailedexplanations. For this case, a quantity of fabrication process reducesand the productivity is improved by high throughput because thereflective electrode and the tilted reflective surface are formed by asingle layer. However, for this construction, there is a possibility offailure as no light emitted from a part of a picture element because thereflective electrode 350 tends to be broken on the ridge of the bank 500if the picture element is segregated into a plurality of light emittingareas.

FIG. 31 shows a planar view showing a part the display device of anembodiment of this invention. It shows a unit picture element composingof one of additive primary colors given by a red-color emission pixel, agreen-color emission one and blue-color emission one therein. In thisinvention, it features that a portion of the bank 500 that segregatesthe picture element into a plurality of areas as shown in the aboveembodiments is eliminated so that the areas are combined into a singleflat surface. Therefore the picture element is formed into a flatsurface of which portions are linked by flat surface 550 which is thesurface on which no bank portion exists. In other words, the reflectiveelectrode, the organic layer and the transparent electrode is formed ina single flat plane without riding over the step difference caused bythe bank. Therefore, as explained in the above embodiment by using FIG.30, the connection of the electrode is maintained by the flat plane areaeven for the construction that the electrode may be cut on the ridgelineof the bank and the failure such that no light emits from a part of areaof the picture element does not tend to occur. In other words, thefailure of electrode break is prevented by eliminating a portion of thebank to make a single combined flat plan in the picture element.

The Ninth Embodiment

Next, we explain another embodiment of this invention. FIG. 32 shows across sectional view of a picture element explaining another embodimentof the display device according to the present invention. Thisembodiment is the display device wherein a modification is applied tothe embodiment explained in FIG. 1 such that the organic layer that isdivided into a red-color pixel, green-color one and a blue-color one ismade a single blue-color organic layer and the optical waveguide layeron the area of the red-color pixel and that of the green-color pixelhave color changing medium layers as red-color fluorescence andgreen-color fluorescence are generated by the illumination of theblue-color light emission from the single blue-color organic layer,respectively. Since the other constructions are same as the aboveembodiment, we use the same signs and notations for the same portionsand omit detailed explanations. Several methods for full color OLEDdisplay has already been proposed and proven several methods for fullcolor OLED display, among which there is a technical method combiningblue light-emitting element and fluorescent color changing media (calledCCM method, hereinafter). The CCM method is to excite the fluorescentdye layer by blue light emitting from blue light emitting layer andobtain the green light and the red light converted thereby, resulting tomake three primary color lights. (see The journal of the institute ofimage information and television engineers, Vol. 54, No. 8, pp.1115-1120).

Next, we explain another embodiment of this invention by applying theCCM method. The picture element that emits blue light is formed, as sameas the above embodiment, with a single optical waveguide layer, howeverthe picture elements which emit red and green lights are formed with thefirst optical waveguide layer 601, the color changing medium layer 602and the second optical waveguide layer 603 stacked in this order in thebasin area surrounded by the bank 500.

The first and the second optical waveguide layers can consist oftransparent resin or transparent inorganic material such as siliconnitride, silicon oxide, titanium oxide, etc. It is desired that therefractive index of the first optical waveguide layer 601 is larger thanthat of the transparent electrode 200. Because the light emitting fromthe organic layer 100 and penetrating the transparent electrode 200 doesnot totally reflect at the boundary surface between the first opticalwaveguide layer 601 and the transparent electrode 200 and is led intothe color changing medium layer 602 with high efficiency, so that we canobtain a large external coupling efficiency by the large amount of thedesired light converted in the color changing medium layer. We can usetitanium oxide as the higher refractive optical waveguide layer materialthan ITO or IZO.

It is important that the heights of the color changing medium layer andthe second optical waveguide layer are lower than that of the tiltedreflective surface. In this case, the light of the light emitting fromthe color changing medium layer propagates in the optical waveguidelayer when it is emitted in almost parallel to the surface of theoptical waveguide layer, and then some portion of the light is reflectedon the tilted reflective surface and goes towards the viewer 1000 as animage picture light. This reflection raises the external couplingefficiency. We can prevent the optical cross-talk and blur since thelight emitting from the color changing medium 602 does not travel intoother picture elements and no light travels through the other pictureelements and reaches to the viewer 1000 after the reflection at thetilted reflective surface surrounding the other picture elements.Therefore we can obtain clear images and pictures and high qualitypicture is realized. Though we can obtain an improvement of the externalcoupling efficiency without the second optical waveguide layer 603, itis important to have a gap 950 which has the similar refractive index tothe air between the color changing medium layer and seal-off material.Because in case of no gap, the light of the light emitted from the colorchanging medium layer partly travels into the seal-off material and islost therein, or partly propagates into other picture element and comesto the viewer 1000 which results in the optical cross-talk and blur.

Next, we explain another embodiment of this invention. The embodiment isthe one wherein a modification is applied to the above embodimentsexplained by referring to FIG. 1 and FIG. 2 such that the organic layerthat is separately designed for a red-color light emitting pictureelement, green-color light emitting one and blue-color light emittingone is all used for a white-color light emitting form the organic layer,the red-pigment, green-one and blue-one are mixed and dispersed in theoptical waveguide layers corresponding to the red-color, the green-colorand the blue-color lights emitting picture elements, respectively. Sincethe other constructions are same as the above embodiment, we omitdetailed explanations for the portion that has the same function.

There are two kinds of the constructions; the organic layer that emitswhite-color light as stacked layers of which each layer has differentlight emission for each other and a single layer that includes differentdoped dies that emit different color lights. An example for the formeris a combination of TPD and partly doped Alq3 with Nail red and1,2,4-triazole derivative (TAZ). An example for the latter is doped PVKwith three kinds of dopants, for example 1,1,4,4-tetraphenyl-1,3butadiene, coumarin 6, DCM1. For either material, the white-color lightemitting organic layer which has high emission efficiency and long lifeis desirable.

The optical waveguide layer is, as same as the embodiment explained byreferring to the FIG. 16B, formed by blowing the optical waveguide layercompound material from the ink-jet head 850 to the basin area surroundedby the bank 500. In this embodiment, the optical, waveguide layercompound includes pigment other than solvent and transparent binderresin. As for the pigments included in the optical waveguide layer whichis formed with the optical waveguide layer compound blown are mixed anddispersed for each picture elements as red, green and blue pigments forthe picture elements for red-, green- and blue-colors, respectively. Wecan exploit those pigments used for the color filters applied to liquidcrystal display devices.

In this embodiment, the white-color light emitted from the organiclayer, directly or after reflecting on the reflective electrode, travelsinto the optical waveguide layer and the light of which wave-length isdifferent from the spectrum of the color of the included pigment filtersis mostly absorbed, though, for example, the light which has thewavelength corresponding to the red-color light can penetrate theoptical waveguide layer which corresponds to the red-color pictureelement due to inclusion of such pigment. Therefore, the light thattravels to the viewer after penetrating the optical waveguide layer ortraveling in the optical waveguide layer and then reflecting on thetilted reflective surface is the red light provided it emits from thepicture element designed for the red-color light emission. Similar tothe red color picture element for the picture element designed forgreen-color or blue-color light emission, we can obtain the lights ofthese colors. For this embodiment, we need simply one organic layer, theprocess features to be easy fabrication since no coloring from suchthree primary colors for each picture element. In addition, as same asthe above embodiments, we can improve the external coupling efficiencyby the effects of the optical waveguide layers and the tilted reflectivesurface and obtain high quality image which has no optical cross talkand does the clear image.

In the embodiments we have discussed, we have shown so-called activematrix type display devices such as the presentation of the image isdone by controlling the operation of a plurality of light-emittingdiodes that compose a plurality of picture elements aligned in aformation of matrix with use of driver elements, however this inventionis not confined in such embodiments. In other wards, the constructionthat has improved the external coupling efficiency shown in the aboveembodiment can be applied to those display devices so-called passivematrix type and to merely illuminating devices. As for the lightemitting elements, it is obvious that the device that light-emits in themedium which has larger refractive index than the air and that has aflat plan in at least a part of the light emitting layer, such asinorganic electro-luminescent devices or inorganic light emittingdiodes, can be applied to this invention.

The invention claimed is:
 1. A display device comprising: a plurality oflight-emitting elements aligned on a TFT substrate in a formation of amatrix, the plurality of light-emitting elements each having a flatsurface portion and including an anode, a light-emitting layer arrangedon the anode, and a cathode arranged on the light-emitting layer; aninsulation layer formed on the TFT substrate and under the lightemitting element; and a tilted metal is provided on a peripheral areasurrounding the flat surface portion of the light-emitting element andhas a tilt angle against the flat surface portion of the light-emittingelement; wherein the tilted metal is provided on a surface of a slope ofa bank that is provided on the insulation layer, wherein a width of across section of the bank becomes smaller as the cross section comesfarther away from a surface of the TFT substrate, wherein a countersubstrate is placed on the plurality of light-emitting elements, thetilted metal, and the TFT substrate, wherein the light emitting elementemits light in a direction from the TFT substrate to the countersubstrate, and wherein gap exist between the light emitting element andthe counter substrate.
 2. The display device according to claim 1,further comprising a predetermined metal between the TFT substrate andthe insulation layer; and an extended metal is connected to the anode,wherein the display device comprising a plurality of pixels aligned onthe TFT substrate in a formation of a matrix, wherein the tilted metalis connected to the cathode, wherein the predetermined metal isconnected to the extended metal via a contact hole in the insulationlayer, wherein each of the bank and the tilted metal overlaps theextended metal and the contact hole in plan view, and wherein each ofthe plurality of pixels includes each of the plurality of light-emittingelements.
 3. The display device according to claim 1, wherein an opticalwaveguide layer is overlaid in an area surrounded by the tilted metal onthe light emitting element.
 4. The display device according to claim 3,wherein the optical waveguide layer has a cross sectional formation sothat a cross sectional width of the optical waveguide layer becomeswider as distance from the surface of the TFT substrate increases, andwherein a height of the tilted metal from the flat surface of thelight-emitting layer is larger than a maximum height of the opticalwaveguide layer.
 5. The display device according to claim 1, whereininactive gas is arranged in the gap.
 6. The display device according toclaim 2, wherein the bank is sandwiched between the tilted metal and theanode in the peripheral area surrounding the flat surface portion of thelight-emitting element, and wherein the bank isn't arranged on the flatsurface portion of the light-emitting element in plan view.
 7. Thedisplay device according to claim 6, further comprising: a plurality ofdriver elements each connected to each of the light-emitting elements; aplurality of capacitor elements each of which is connected to each ofthe light emitting elements and receives each of a plurality of imagesignals; and a plurality of switching elements each of which isconnected to each of the capacitor elements and each of the lightemitting elements and controls input of each of the plurality of imagesignals to each of the capacitor elements, wherein the predeterminedmetal is connected to the driver element.
 8. A display device comprisinga plurality of light-emitting elements aligned on a TFT substrate in aformation of a matrix, at least one of the plurality of light-emittingelements having a flat surface portion and including an anode, alight-emitting layer arranged on the anode, and a cathode arranged onthe light-emitting layer; an insulation layer formed on the TFTsubstrate and under the light emitting element; a first metal isprovided on a surface of a slope of a first bank that is provided on theinsulation layer; and a second metal is provided on a surface of a slopeof a second bank that is provided on the insulation layer, wherein theflat surface portion of the light-emitting element is arranged betweenthe first metal and the second metal, wherein a width of a cross sectionof each of the first and the second banks becomes smaller as the crosssection comes farther away from a surface of the TFT substrate, whereina counter substrate is placed on the plurality of light-emittingelements, the first metal, the second metal, and the TFT substrate,wherein the light emitting element emits light in a direction from theTFT substrate to the counter substrate, and wherein gap exist betweenthe light emitting element and the counter substrate.
 9. The displaydevice according to claim 8, further comprising a predetermined metalbetween the TFT substrate and the insulation layer; and an extendedmetal connected to the anode, wherein at the flat surface portion of thelight-emitting element, the anode is connected to the organic layer, andthe organic layer is connected to the cathode, wherein the first metaland the second metal are connected to the cathode, wherein thepredetermined metal is connected to the extended metal via a contacthole in the insulation layer, and wherein each of the first bank and thefirst metal overlaps the extended metal and the contact hole in planview.
 10. The display device according to claim 9, wherein an opticalwaveguide layer is overlaid on the flat surface portion of thelight-emitting element.
 11. The display device according to claim 10,wherein the optical waveguide layer has a cross sectional formation sothat a cross sectional width of the optical waveguide layer becomeswider as distance from the surface of the TFT substrate increases, andwherein a height of the first metal from the flat surface portion of thelight-emitting element is larger than a maximum height of the opticalwaveguide layer.
 12. The display device according to claim 8, whereininactive gas is arranged in the gap.
 13. The display device according toclaim 9, wherein the first and the second banks are formed in anintegrated manner, wherein a peripheral metal of the anode as thepredetermined metal surrounds the flat surface portion of thelight-emitting element in plan view, and wherein the first bank isarranged between the first metal and the peripheral metal of the anode,and the second bank is arranged between the second metal and theperipheral metal of the anode.
 14. The display device according to claim13, further comprising: a plurality of driver elements each connected toeach of the light-emitting elements; a plurality of capacitor elementseach of which is connected to each of the light emitting elements andreceives each of a plurality of image signals; and a plurality ofswitching elements each of which is connected to each of the capacitorelements and each of the light emitting elements and controls input ofeach of the plurality of image signals to each of the capacitorelements, wherein the peripheral metal is connected to the driverelement.
 15. The display device according to claim 13, wherein the firstmetal is provided on a peripheral area surrounding the flat surfaceportion of the light-emitting element and has a first tilt angle againstthe flat surface portion of the light-emitting element, wherein thesecond metal is provided in the peripheral area surrounding the flatsurface portion of the light-emitting element and has a second tiltangle against the flat surface portion of the light-emitting element,and wherein the first and the second banks includes the peripheral areaformed on the peripheral metal of the anode.
 16. A display devicecomprising: a plurality of light-emitting elements aligned on a TFTsubstrate in a formation of a matrix, at least one of the plurality oflight-emitting elements having a flat surface portion and including ananode, a light-emitting layer arranged on the anode, and a cathodearranged on the light-emitting layer; an insulation layer formed on theTFT substrate and under the light emitting element; and a metal isprovided on a surface of an insulation bank that is provided on theinsulation layer, wherein each of the insulation bank and the metalsurrounds the flat surface portion of the light-emitting element in planview, wherein a width of a cross section of the insulation bank becomessmaller as the cross section comes farther away from a surface of theTFT substrate, wherein a counter substrate is placed on the plurality oflight-emitting elements, the metal, and the TFT substrate, wherein thelight emitting element emits light in a direction from the TFT substrateto the counter substrate, and wherein gap exist between the lightemitting element and the counter substrate.
 17. The display deviceaccording to claim 16, further comprising a predetermined metal betweenthe TFT substrate and the insulation layer; and an extended metalconnected to the anode, wherein at the flat surface portion of thelight-emitting element, the anode is connected to the organic layer, andthe organic layer is connected to the cathode, wherein the metal areconnected to the cathode, wherein the predetermined metal is connectedto the extended metal via a contact hole in the insulation layer, andwherein each of the insulation bank and the metal overlaps the extendedmetal and the contact hole in plan view.
 18. The display deviceaccording to claim 17, wherein a peripheral metal of the anode as thepredetermined metal surrounds the flat surface portion of thelight-emitting element in plan view, and wherein the insulation bank isarranged between the metal and the peripheral metal of the anode. 19.The display device according to claim 17, further comprising: aplurality of driver elements each connected to each of thelight-emitting elements; a plurality of capacitor elements each of whichis connected to each of the light emitting elements and receives each ofa plurality of image signals; and a plurality of switching elements eachof which is connected to each of the capacitor elements and each of thelight emitting elements and controls input of each of the plurality ofimage signals to each of the capacitor elements, wherein thepredetermined metal is connected to the driver element.
 20. The displaydevice according to claim 18, wherein the metal is provided on aperipheral area surrounding the flat surface portion of thelight-emitting element and has a tilt angle against the flat surfaceportion of the light-emitting element, and wherein the insulation bankincludes the peripheral area formed on the peripheral metal of theanode.